The field of application for current industrial robots is limited. In one typical application, collection and delivery points must be well-defined. Another application, machining of workpieces, requires that the workpieces be identical.
These and other limitations can be reduced by the introduction of so-called sensor control. "Sensor control" is a method of control in which information from transducers (sensors) on the robot arm is used for controlling the arm. Such transducers may, for example, be arranged to sense the forces exerted on the robot, or the deviation in the position of a robot arm from a contour or an object. An industrial robot having sensor control is the subject of U.S. Pat. application Ser. No. 692,553, filed June 3, 1976, now U.S. Pat. No. 4,076,131 the subject matter of which is incorporated by reference.
The introduction of sensor control has so far been restricted as a result of increased complexity of the control system. Generally, the sensing directions of transducers do not coincide with the directions of movement (degrees of freedom) of the robot. Accordingly, a complicated coordinate transformation must be made between the coordinate system of the transducers and the coordinate system of the robot itself.
In point-to-point control, the complexity of the control system is substantially independent of the geometry of movement of the robot arm if the displacement is performed along a smooth even curve line.
On the other hand, if either the displacement is prescribed (i.e., rectilinear), or is to be influenced by signals from sensors, the geometry of movement of the robot arm will greatly influence the complexity of the control system.
Of the four most frequently used coordinate systems for robots--Cartesian, cylindrical, spherical and anthropomorphic--the anthropomorphic system is the most complex one from the point of view of control.
A robot with an anthropomorphic coordinate system is disclosed in the above-mentioned U.S. Pat. application Ser. No. 692,553, see FIG. 1.
The difficulty in achieving a certain control function depends on the relation between displacement in a coordinate and the control signal, as well as the type of coordinate system.
Generally, for sensor control, the output signal from a sensor (one dimensional) is used for simultaneous correction or control of several of the coordinate axes of the robot.
The n-dimensional correction (n=number of degrees of freedom of the robot system) of robot movement corresponding to the sensor signal, may in principle be calculated if the following is known:
sign and amount of sensor signal PA1 the relation between sensor signal and displacement PA1 the orientation of the sensor PA1 the position of the robot arm.
Generally, such a calculation, especially in anthropomorphic coordinate systems, requires a very high calculational capacity of the control equipment because of the complicated coordinate transformations.
The possibility of introducing sensor control without essentially influencing the complexity of the control system depends on the choice of sensors, the relation between their sensing directions and the robot movement coordinate system.
It is important to arrange the apparatus so that flexibility in applying different sensor functions is facilitated.
The present invention aims to provide a control method including sensor control, which considerably reduces the required calculating capacity of the control system.